1. Field of the Invention
The present invention relates to apparatus for protecting AC power lines, telephone lines and coaxial transmission lines and, more particularly, to apparatus which provides protection for those lines in a single enclosure which contains an AC power meter and a common ground.
2. Discussion of the Related Art
In the past few years more and more homes have begun using sensitive electronic equipment as telecommuting and conducting business from one's home has become more commonplace. In addition to home entertainment centers with expensive audio/visual equipment, many homes now have personal computers, modems, printers, copiers, facsimile machines, telephone answering systems and home security systems. This sensitive electronic equipment is connected to the outside world by means of telephone lines (both conventional and high speed data lines), coaxial transmission lines (both cable TV and satellite dish antenna) and AC power lines.
Telephone lines are traditionally protected by surge arrestors located in network interface devices mounted on the sides of homes. See devices 73 in FIG. 3 of U.S. Pat. No. 4,979,209 issued to Collins et al on Dec. 19, 1990. Grounding for these overvoltage protection devices is provided by means of an earth ground brought into the enclosure at the time of installation and attached to ground bus 71 at terminal 71A.
Coaxial transmission lines carrying cable television signals may also be brought into homes through network interface devices. See U.S. Pat. No. 3,394,466 issued to Schneider et al on Feb 28, 1995. As shown in FIG. 1 of that patent, the coaxial cable is grounded by connecting a ground strap 228 from module 220 to ground bus 71 which is then connected to earth ground. See column 4, lines 50-54. Coaxial surge arrestors for protecting coaxial transmission lines from overvoltage conditions are also known. See U.S. Pat. No. 4,616,155 issued to Guichard on Oct. 7, 1986 and U.S. Pat. No. 5,566,056 issued to Chaudhry on Oct. 15, 1996.
It is also known to protect sensitive electronic equipment by providing overvoltage protection for AC power lines. Secondary surge arrestors which plug into wall outlets and accommodate a series of male electrical plugs are in common use. The assumption made in using such devices is that they are properly grounded. A device which plugs into a wall outlet and provides protection for telephone lines is also known. See U.S. Pat. No. 4,438,477 issued to Cawley on Mar. 20, 1984.